Continuous-tunnel kiln



AprilV 3o, 1929. T. G. MCDOUGAL f 1,710,995 l Y l -CNTUWO'U'S TUNNEL KILN file d'Mamh 11, 1925 ao? neg/J Patented Apr. 30, l19429.

UNITED. STATES "1,710,995 PATENT 'o-luucE.4`

mmm: G. Menouonn, or FLINT, MICHIGAN, AssIGNoR To n C sPARx nuo COMPANY,

-oF FLINT, MICHIGAN, A coMPANY or MICHIGAN.

CoNrINUoUssTUNNEL THIN.

Application -iled-.lliiarch 11, 1925. Serial No. 14,745.

This is an improvement on the invention' y disclosed in my Patents Nos. 1,416,726 and fkiln containing a preheating zone, a high temperature zone, and a cooling zone. The prelizninaryheating 1s done 1n the preheatlng zone. In the high temperature zone the Wares are exposed to the direct ac tion of the intense heat produced by vthe substantially flameless combustion of premixed air and fuel, thel products -of combustion lpassing' outwardly through the preheating zone and serving as the hcatinglneans therefor. Beyond the high L tennieiature Zone and separated from it by a baflie 'is a cooling zone" Where the wares are subjected to decreasing temperatures preparatory to theirdscharge. Thus the wares are exposed to temperatures varying from a minimum at the tunnel entrance, increasing as the scat of'combustion is approached, reaching a maximum'in the high temperature zone and again decreasing throughout the Vcooling' zone. Y

In the practical operation of kilns embodying the features herein briefiy referred to and set forth more at length in my prior patents, it was vfound that the speed with which the ware could be fed into the kiln was limited vto that speed below which no cracked ware would result. The moreintricate the shape of the ware the more prolific was the cracking defect for any given rate of feed.

It is a primary object ofthe present invention to improve the. continuous lnln method of burning ceramic wares by `eluninating the conditions which have heretofore resulted in a high percentage of fractures requiring for remedy an uneconomical increase in the time of tiring. I

Now it was heretofore known that there is a certain stage in the burning of ceramic wares between the temperatures of 932 F. and 1292" E. which -is very critical inasmuch as the "clay shapes between these temperatures are inthe process of losing water of crystallizationfrom the clay bond-'and are weaker mechanically7` than at `any other time during their processing. It is especially inadvisable at or near this stage of the burning process to allow the Ware to be subjected to a sudden risefin temperature. In an effort to ascertain whetherthe wares were subjected to any such sudden increase inv temperature in the continuous kiln process as heretofore carried out, a .th-crmo4couple Was passed up through lthe refractory bottom of the travelling car.

used -for conveying the Ware through the kiln so that the bead of the thermo-couple occupied the same position as a piece of ware and it was thus carried throughout the length of the kiln.` 'Ihe thermo-couple wastconnected with a recording pyrometer. vIt was discovered that at periodic intervals in the preheating zone the pyrometer recorded sudden increases in rate' of temperature rise followed by a short period in-which no rise occurred. It was foundcthat'these violent fluctuations occurred when thethermo-couple was passed under one of the widely separated drop arches or baiiles of the kiln, clearly shown at 9 in Figure l of m Patent 1,416,726;

These drop arches or ba es, it may be explained, are an outgrowth of the common forni of continuous kiln construction heretofore used. For convenicnce and economy in construct kilns for continuous work of arch formation. This carried with it the disadvantage that in the preheating zone the hot gases would travelalong the vault of the arch and would be ineffective to give the'required preparatory heating to the Ware, and it was therefore necessary to make use of drop arches or baffles. As will be apparent by reference to my prior patent, the upper. parts of these drop arches were of a radius to con,- form to the brick arch construction spanning the Width of the kiln opening on certain rowlocks of which they were partially suspended. The bottoms of these arches were in a horizontal plane parallel -to the tops of the conveying means passing through the. tunnel and' served as bailes to deflect the hot gases emerging from the high temperature chamber down upon the ware in the preheating zone.

Accordingly, an object of my improvement is, specifically,^to so construct acontinuous tunnel kiln as'to avoid the violent fluctuations in temperature heretofore encountered.

'In the embodiment of the invention herein obstructed surface thus insuringuniformity' Afind application in otliei"relatioiis.

4in heat distribution and a smoothly tapering trol the passage .of heated. gases through the i kiln in order that they may effectively impinge upon the articles to be treated, said means being adjustable to accommodate the heat flow to articles of different sizes. Speciiically this means consists of removable baf fles ,of yrefractory material preferably ar ranged on the undei side of the roof of the kiln; It 'will be evident that these baffles,

Y when used-7 constitute, in effect, so .far as heat distribution' is concerned, a substantially eontinuous drop arch for the humps in the temperature gradient become of correspondingly diminishing magnitude as the number of baiies is increased and hence this construction comes within the broad scope of theol)- ject of invention first stated.

As a further object of my invention in adapting a liiln of this type to the burning of ceramic wares of different sizes, I have pro lvided means for adjustment of the baffles customarily used between the high temperature zoneand the cooling Zone, although it is obvious that this phase of my invention may- Speeifically, this means consists in the provision ofv auxiliary baffles constituted by thin plates of refractory material which may be used interchangeably to increase the effective rarea of the baflie.

. Other and further'objects of my invention y will appear from the .following description.

In the drawings:

Figures l and la are central, vertical, longitudinal sections each showing substantially one half the length of the kiln, Figure l being at the charging end;

Figure 2 is a section .on line 2-2 of Figure la;

Figure Seis a section of one form ofbaflle whileFigure t discloses a modification.

The showing of the drawing'is of course merely illustrative of one form of construetionof kilnwhich may be 'employed and may be varied as desired. In this embodiment, l indicates the preheating zone,2 the high temperature zone, and 3 the cooling zone. As the temperature in these three zones,` except as otherwise herein stated, is maintained and controlled in substantially the same manner as set forth in my prior Patentv 1,416,726, no description of the means employed for these purposes will be given. At l are shown the usual cars carrying the ceramic wares and travelling upon the tracks 5.

It will be observed upon reference to Figure 1 that' the construction of the preheating zone of the `tunnel is such that substantially uniform clearance is maintained between the roof of the tunnel and the cars, thus insuring uniformly tapering heat variation throughout this portion of the passage. In the form shown in this ligure, Ythis object is attained by providing this section of the. tunnel with aroof consisting of a flat slab 6 l calcined diatomaceous earth (liieselguhr) with Portland cement in the proportion by weightof 138 parts liiesclguhr to lOOparts of cement will produce a composition which will providethe desired characteristics and be serviceable for temperatures below ap proxiinately 1600o F. Of course it is to be understood that broadly my invention is not limited to the use of this particular material Vif other suitable compositions may be sub sequentlydiscovered. i

IVliile in this embodiment of the invention I have shown the use of a tunnel construction which promotes uniform nonfluctuating temperature variations only in the preheating zone, it is'to be lunderstood that its Vapplicability is not to be so limited but that this same means maybe effectively employed where ever itis found desirable to provide for a uniform'temperature gradient in the treatment of articles. 4

It will be observed thatthe under surface of the slab 6 is provided with guide-ways 7 constituting engaging means for the reception s of plates S of refractory material, one of which is shown in Figure 3. A series of these. plates is provided, graduated in size. They are to be used interchangeably and their function is to reduce the effective clearance between the cars and the roof ofthe tunnel so that the kiln may be used with articles of different sizes, as stated heretofore in the ob- 'jects of the invention. It will be observed that these battles are closely spaced with consequent reduction in the temiierature drop between them. Owing to 'this factfand to ltl'ie further fact that theextiut of projection of 'the battles into the tunnel is slight coni-A pared with the extent of projection of the batlies 9 lininy prior patent, the humps in the temperature gradient are reduced and the construction becomes the equivalent of a substantially continuous drop arch thus avoiding` the obj eetionably violent changcsin temperature found to exist under prior practices.

iVhile I have shown the application of bafes to the top wall roof only of the tunnel it 'is' te be understood that their use is not. so limited but they may be applied wherever it is 'desired to control the flow of thelheated gases for the purposes stated.

As inthe construction inv my prior Patent 1,416,726 it will be observed by reference to the provision of an opening 14 in the tunnel,

i guide-Way 1I in which areslidably received thi-n plate-like supplemental hafile members 8, as more clearly shown in Figure 3.

As. an alternative'metliod I have shown in Figure Il. the baille 10 provided with a groove or ledge upon its side upon which are hooked the upperv ends of plate-like supplemental battle members 13- of the same material and lperforming the same functions as plates 8.

It will be noted 'that these plates 1 3 are located 'on the discharge side .of the main baille member-10 with the result-ant advantage that in the case 'of a jamming of Wares inpassing through the tunnel the baille willy be merely lifted ofi its support and carried along with the Wares Withoutdamagexto the permarientl tunnel structure.

' As Will be observed by reference to Figure 2, the placing in positionof. these supplemental baille members 8, whether used in the preheating Zone orbetween the high temperature. zone and the cooling zone, is facilitated bv Wall opposite the guidevvay which is to re-i ceive them. After they have been properly positioned thesel openings' are temporarily filled in to avoid loss of heat. By this means the refractory pieces can be inserted from outside of the kiln Without interrupting its operation.

Where I have made use of the phrase continuous tunnel kiln it is to be understood that I have reference to a tunnel kiln in which the continuous process of burning is employed and which may or may not be in the form of a continuous or closed curve.

Where I have referred to one of the walls as constituting a heat reflecting surface it is to be understood that the phrase does not have reference to reflection by radiation only but also to the control of heat through the control of the passage of heated gases through the tunnel.

While Ihave shown and described one illustrative embodiment of my invention, it is to be understood that I am not to be ylimited thereby, but only to the extent called for by the terms of the appended claims.

`1. In a continuous-tunnei'kiln for burning ceramic wares, having a zone of graduated heat treatment in which. the wares are subv stantially single tier formation, said tunnel having substantially unbroken uniplana'r Walls throughout said zone, said means and tunnel being so arranged as to permit the passage of a substantiallyunbroken stream of gases therethrough in a direction oppositeto the direction of travel of the Wares and in a path substantially parallel thereto, so a's to promote a steady non-fluctuating rate of temperature change throughout the said zone' of graduated heat treatment.

2. In a continuous tunnel kiln for burning ceramic 'Wares by subjecting saidl wares to direct contact with hot combustion gases, said kiln having a zone of graduated heat treatment, one of" the walls ofsaid tunnel functioning chiefly as a heat reflecting surface, means moving through the said kiln for cariying 'Wares being burned therein, said wall being uniplanar so'V as to provide uniform clearance between the heat reflecting surfacev -and .the wares throughout the zone of grad-4 uated heat treatmentfor the passage of hot gases in a direction substantially parallel f to the path of the wares thereby subjecting the wares to steady non-fluctuating temperature variations.

3. A continuous tunnel kilnfor Lburning ceramic Wares comprising, in part-,fia graduated heat treatment zone through which pass hot gases in direct Contact with the Wares,

said zone being provided With a flat uniplanar roof of highly refractory material serving as the main heat reflecting surface and means. for passing 'wares in single tier formation through said tunnel, said tunnel and Wares beico ing so arranged as to afford substantially uniform clearance between said wares and the said heat reflecting surface throughout the said 'graduated heat `treatment zone.

4. A continuous tunnel kiln for burning ceramic wares including a pre-heatingzone,

a high temperature zone, and a cooling zone,

means for passing a stream of hot gases through said pre-heating zone in contact with said Wares in a direction opposite to that. in which the Wares travel through said kiln and substantialLy7 parallel thereto, the portion vof the'tunnel serving as the preheating zone being provided with a uniplanar roof of refractory material affording substantially uni form clearancebetween said roof and the wares passing through said tunnel whereby to facilitate al steadynonfluctuating temperatui'e rise throughout the critical period of heat treatment.

5., In a continuous tunnel kiln for burning ceramic wares, having a wall functioning as a heat reflecting surface, heat @fleeting-.

means adapted to be removably secured to said wall for varying the heat distribution along said wall.

6. In a continuous tunnel'kiln for burin ing ceramic wares in which a stream of heated gases travels therethrough, means adapted to be secured to one of the walls ofsaid tunnel for varying' the clearance between said vwall and the wares carrying means passing through said tunnel for dellecting the gases upon the wares thereonpermitting the use of said tunnel kiln for articles of varying size. 7. In tlie combination asspecilied in claim 6,-said last named means comprising intere.

line with said engaging means te permit the introduction of said heat deflecting means into said tunnel and its connection with said engaging means.

10. A continuoustunnel kiln having zones for varying' heat treatment and a baille located between certain of said zones, said baffle being providedwit-h means for adjusting the extent of its projection into said tunnel.

11. In the combination as set forth in claim 10, a portion of said baffle being provided.V

with a guide-way and said means comprising pla tes having portions for engaging said guide-way. y

, In testimony 12. In'the combination set forth in claim 10, portion of said baille being provided with a guide-way facingtoward the discharge end ofsaid tunnel and said means comprising plates adapted to `cooperate with said guidewayd whereby in case the wai'es become jammed in passing-` through the tunnelsaid 1 plate will be disengaged' from said guideway without damage to the tunnel structuie.

13.l A, furnace wall element constituted of a composition of substantially 138 parts of kieselgulir to 100 parts of Portland cement.

14. In a continuous tunnel kiln for burning ceramic wares of the type in which the wares are 'subject to the direct action of gases foreii'ecting temperature changes7 and having a top wall or roof and. a bottom or bed, means for passing wares therethrough, and means for varying the effective-distance between the ioof of said tunnel and said bed for defleeting gases upon the wares thereon adapting. the

tunnel for use with articles of varying size.

15. In a continuous tunnel kiln for burning ceramic wares having a preheating zone in which the wares aie subjected to the direct action ofl liet combustion gasesrpie paratory toliurning,l means for' transporting Wares through'tlie kiln, adapted to support the wares in single tier formatioin the kiln throughout said Zone being provided with a flatuniplanar roof of refractory mater-ial providing substantially uniform clearance between' the roof and the Wares passing through the tunnel whereby to facilitate a steady temperature rise throughout the eritical pre-heating treatment.

whereof I affix my signature.

TAINE G. MCDOUGAIL. 

